A 2 year old female spayed Ragdoll cat presented to her local veterinarian for tachypnea. The referring veterinarian diagnosed the patient with chylothorax based on her severe respiratory distress, radiographic changes and thoracocentesis results. The patient was then referred to Cornell University Hospital for Animals for further workup. On presentation the patient was tachypneic with an increased effort and bilateral crackles. A thoracocentesis revealed an opaque effusion from the pleural cavity which had an elevated triglyceride level when compared to serum levels, confirming it as chylous. Based on the results of blood work, cardiology consult, abdominal ultrasound, and CT scan a diagnosis of idiopathic chylothorax was made. When the patient continued to do poorly, she was taken to surgery where a thoracic duct ligation, pericardectomy and lung biopsy were performed successfully. The biopsy results showed a severe pneumonia, atelectasis, and fibrosing pleuritis. A chest tube was placed intra-operatively and the patient was started on a low fat diet, antibiotics, pain medication and Rutin therapy. After the cat’s clinical signs improved, her chest tube was pulled and she was discharged to the care of her owners. The patient’s prognosis remained poor due to the presence of severe pneumonia and fibrosing pleuritis.